scholarly journals Vertical Metallicity Gradient of the Galaxy Based on UBV Starcount Data

1994 ◽  
Vol 161 ◽  
pp. 420-422
Author(s):  
T. Yamagata ◽  
Y. Yoshii
Keyword(s):  
Spatial Distribution ◽  
Least Squares ◽  
High Latitude ◽  
Vertical Gradient ◽  
Thin Disk ◽  
Thick Disk ◽  
The North ◽  
The Galaxy ◽  
Metal Abundance ◽  
North Galactic

The spatial distribution of metal abundance in the Galaxy has been analyzed using the UBV starcount data recently obtained in two high-latitude regions of the North Galactic Pole (NGP) and Selected Area 54 (SA54). A least-squares analysis was performed to determine the vertical metallicity gradient for each of the thin and thick disk components that gives a reasonable fit to the observed U-B and B-V colour distributions to V = 18 mag. The most probable value of the vertical gradient is obtained as d[Fe/H]/dz = −0.5 kpc−1 for the thin disk, and −0.1 kpc−1 for the thick disk.

scholarly journals Solar Neighbourhood Age–Metallicity Relation Based on Hipparcos Data

2004 ◽  
Vol 21 (2) ◽  
pp. 121-125 ◽  
Author(s):  
Akihiko Ibukiyama
Keyword(s):  
Star Formation ◽  
Essential Feature ◽  
Formation Rate ◽  
Vertical Gradient ◽  
Thin Disk ◽  
Thick Disk ◽  
Solar Neighbourhood ◽  
Orbital Parameters ◽  
The Galaxy ◽  
The One

AbstractWe derive age–metallicity relations (AMRs) and orbits for the 1658 solar neighbourhood stars for which accurate distances are measured by the Hipparcos satellite. The sample comprises 1382 thin disk stars, 229 thick disk stars, and 47 halo stars according to their orbital parameters. We find a considerable scatter for thin disk AMRs along the one-zone Galactic chemical evolution (GCE) model. Orbits and metallicities of thin disk stars show no clear relation to each other. The scatter along the AMR exists even if stars with the same orbits are selected. We examine simple extensions of one-zone GCE models which account for inhomogeneity in the effective yield and inhomogeneous star formation rate in the Galaxy. Both extensions of the one-zone GCE model cannot account for the scatter in the age–[Fe/H]–[Ca/Fe] relation simultaneously. We conclude, therefore, that the scatter along the thin disk AMR is an essential feature in the formation and evolution of the Galaxy. The AMR for thick disk stars shows that star formation terminated 8 Gyr ago in the thick disk. As previously reported, thick disk stars are more Ca-rich than thin disk stars with the same [Fe/H]. We find that thick disk stars show a vertical abundance gradient. These three facts — AMR, vertical gradient, and [Ca/Fe]–[Fe/H] relation — support monolithic collapse and/or accretion of satellite dwarf galaxies as likely thick disk formation scenarios.

scholarly journals The Vertical Structure and Kinematics of the Galaxy

1994 ◽  
Vol 161 ◽  
pp. 435-439
Author(s):  
C. Soubiran
Keyword(s):  
Velocity Distribution ◽  
Vertical Structure ◽  
Vertical Gradient ◽  
Thin Disk ◽  
Thick Disk ◽  
Exponential Density ◽  
The Galaxy ◽  
Local Densities ◽  
Discrete Populations

A sample including 2370 stars with (U, V) velocities has been analyzed up to z = 2.5 kpc. It is shown that the observed vertical gradient in the velocity distribution can be explained by the sum of 3 discrete populations with constant kinematics. The observations are well fitted by exponential density laws for the thin disk and the thick disk with scale lengths of 280 pc and 700 pc respectively, and with local densities of 6% and 0.15% for the thick disk and halo respectively.

scholarly journals A New Sample of Thick Disk and Halo Stars

1995 ◽  
Vol 164 ◽  
pp. 386-386
Author(s):  
C. Soubiran ◽  
M.N. Perrin ◽  
R. Cayrel ◽  
E. Chereul
Keyword(s):  
Stellar Population ◽  
Thin Disk ◽  
Thick Disk ◽  
The Other ◽  
Chemical Characteristics ◽  
Fundamental Parameters ◽  
Halo Stars ◽  
Synthetic Spectra ◽  
The Galaxy ◽  
Comparison Stars

The aim of our stellar population study is to investigate the kinematical and chemical characteristics of the thin disk, thick disk and halo of the Galaxy. We have selected 51 stars in 2 astrometric and photometric surveys at l = 42°, b = +79° (Soubiran 1992) and l = 167°, b = +47° (Ojha et al. 1994), on the basis of the Reduced Proper Motion Diagram. They were observed with the 193cm telescope at Observatoire de Haute-Provence, with the CARELEC spectrograph (dispersion of 66Å/mm, FWHM of 3.0Å, range λλ4600 – 5500Å), together with 43 comparison stars with known fundamental parameters. The derivation of Teff, logg and [Fe/H] was done differentially using a grid of synthetic spectra and the comparison stars, as described in Cayrel et al. (1991). Twenty of the target stars were found to be more deficient than −0.5. In the (V, [Fe/H]) distribution, the halo stars are clearly separated from the other stars with a mean of (V, [Fe/H]) ≃ (−210km/s, – 1.4dex). Because of the small size of the sample, it was not possible to discriminate the thick disk from the thin disk. We have taken 200 more spectra, and with these new observations, we hope to be able to deconvolve the 3 populations in the (U, V, W, [Fe/H]) space as we did previously with the (U, V) velocity (Soubiran 1993).

scholarly journals Deep Multi-Colour Starcounts

1994 ◽  
Vol 161 ◽  
pp. 423-424
Author(s):  
I.N. Reid ◽  
S.R. Majewski
Keyword(s):  
Standard Model ◽  
Stellar Population ◽  
Stellar Populations ◽  
The North ◽  
Halo Stars ◽  
The Standard Model ◽  
The Galaxy ◽  
Best Fitting ◽  
Galactic Stellar Populations ◽  
North Galactic

Starcounts remain one of the most effective methods of probing the structure of the Galactic stellar populations. However, studies of the distribution at large distances above the Plane demand accurate photometry extending to faint magnitudes (V > 20), and such datasets are still rare. We (Reid & Majewski 1993) have analyzed data from one field — Majewski's (1992) UJF observations of SA57, the North Galactic Pole field. Our results revealed significant discrepancies with the standard model of the Galaxy (see refs. in Reid & Majewski), notably a paucity in the number of halo stars by a factor of two and the presence of a factor of two more disk stars than predicted — sufficient stars that the disk is the majority stellar population, outnumbering halo stars 2:1 even at V = 21. Majewski et al. (1993) has obtained UJFN photographic data for several other fields, and Fig. 1 shows a preliminary comparison of these observations with the predictions of the best-fitting SA57 model. Given that none of the parameters have been modified, the agreement is surprisingly good.

scholarly journals Metallicity Structures of the Milky Way

1996 ◽  
Vol 169 ◽  
pp. 427-428
Author(s):  
Roland Buser ◽  
Jianxiang Rong
Keyword(s):  
High Latitude ◽  
Preliminary Analysis ◽  
Milky Way ◽  
Structural Models ◽  
Thin Disk ◽  
Thick Disk ◽  
Abundance Gradient ◽  
Galactic Population

The metallicity-sensitive (U – G) colors from the new homogeneous catalog of photographic RGU data in seven high-latitude fields have been used to determine the larger-scale metallicity distributions of the Galactic population components. For the thick disk, preliminary analysis based on our best structural models provides a mean metallicity 〈[M/H]〉 = −0.6 ± 0.3dex and a marginal vertical metallicity gradient ≈ −0.1dex/kpc. The observed color distributions are further consistent with the (old) thin disk having mean abundance 〈[M/H]〉 = −0.3 ± 0.2dex and abundance gradient ∂[M/H]/∂z = −0.6dex/kpc.

scholarly journals Abundances of α-Process Elements in Thin-Disk, Thick-Disk, and Halo Stars of the Galaxy: Non-LTE Analysis

2019 ◽  
Vol 63 (9) ◽  
pp. 726-738 ◽  
Author(s):  
L. I. Mashonkina ◽  
M. D. Neretina ◽  
T. M. Sitnova ◽  
Yu. V. Pakhomov
Keyword(s):  
Thin Disk ◽  
Thick Disk ◽  
Halo Stars ◽  
The Galaxy ◽  
Process Elements

scholarly journals Stellar Kinematics in the Galactic North Pole Region on the Basis of Tautenburg Schmidt Telescope Plates

1994 ◽  
Vol 161 ◽  
pp. 444-446
Author(s):  
N.V. Kharchenko ◽  
E. Schilbach ◽  
R.-D. Scholz
Keyword(s):  
Spatial Distribution ◽  
Galactic Plane ◽  
North Pole ◽  
Proper Motions ◽  
Stellar Kinematics ◽  
Schmidt Telescope ◽  
The North ◽  
Spatial Velocity ◽  
North Galactic

The spatial velocity components and their dispersions in the Galactocentric and rotation directions, eccentricities of Galactic orbits, parameters of spatial distribution and the change of all these characteristics with distance from the Galactic plane are detennined. These data have been obtained on the basis of absolute proper motions and stellar B, V magnitudes in two sky regions near the North Galactic Pole (NGP) by means of a plate set of the Tautenburg Schmidt telescope.

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